The gold vapor laser appears to be an attractive alternative to existing laser sources for photoradiation therapy (PRT) of malignant tumors. To establish this fact, Plasma Kinetics proposes a six-month study during which the following tasks will be performed: A) the development of a high-power gold vapor laser and delivery system to produce pulsed radiation at 628 nm. B) a determination of the efficacy of such light in the treatment of malignant tumors implanted in the eyes of rabbits, when used in conjunction with hematoporphyrin derivative. The first task will be performed at Plasma Kinetics, where a lower power (less than 2 W) gold laser has already been successfully tested. The second task will be carried out by members of the University of Iowa Cancer Center Phototherapy Group under subcontract with Plasma Kinetics. Initial studies will be performed by Group members at Plasma Kinetics, based on animal tumor irradiation carried out with the existing low power gold vapor laser. These studies will establish whether (as expected) pulsed laser irradiation of hematoporphyrin derivative (HPD)-treated malignant tumors results in necrosis of the tumors (as is the case in the previous studies of continuous (rather than pulsed) laser irradiation at the same wavelength). Final studies (last 2 months) will be carried out at the Univ. of Iowa Laser Facility with the gold laser and delivery system developed by Plasma Kinetics under Task A of the proposed effort. Research in PRT has shown considerable promise for cancer treatment. However before this approach becomes practical on a large scale, simple, reliable light source must exist which can be operated easily by medical personnel. Unlike the conventional argon-laser pumped dye laser, the gold laser promises to be such a device, with a potentially enormous commercial market.